not sure if that could work like that (who knows) but agreed, they would get caught

my understanding is the flow goes: etf buyer -> broker -> AP -> sponsor -> custodian

if the ETF (sponsor) collects net 10B then that is coming from the AP as the middleman (they put the cash in with the sponsor to create the shares, net a fee). sponsor then uses that cash to buy btc and store at a custodian. if the sponsor only buys 1B worth, the AP would know something is up (ignoring liquidity / supply issues) - I'd expect they already have an idea of what the $$/share and NAV should be pre/post the trade getting filled and are expecting to move 10B of new shares back to the broker.

if that's wrong someone please correct me, would love to understand it better